Quantitative Analysis Of Morphology And Its Neotectonic Implication In The Wanchuan Catchment Based On Digital Elevation Models

The moderrn surface form is the common product of the internal tectonic activity and the surface external dynamic process.The quantitative acquisition of the surface morphological features can invert the near-surface tectonic activity process.The development of modern science and technology,especially the emergence and application of 3S technology has made a great contribution to quantitative development of tectonic geomorphology.The geomorphic indexes not only quantitatively describe the surface morphology,but also reveal the traces of regional tectonic activity and help to assess the status of neotectonic activities.Wanchuan River flows from Maxian Mountain into yellow river,located in the northeastern Tibetan Plateau.There are two sets of fault zones in the catchment,namely Maxianshan-Xinglongshan fault systems and Wanchuan River fault.Relatively,Wanchuan River fault is poorly understood,though many studies have been carried out here.In this paper,the geomorphic indexes such as stream length-gradient index(SL)and the Hack profile,the mountain front sinuosity index(SMF)the valley floor height-to-width ration(VF),the basin asymmetry(AF)and basin hypsometry index,were used to quantitatively analysis landform features.In addition,the geological data and field exploration data were combined with the geomorphic indexes to comprehensively assess the tectonic activity state.The results are as following:1)The knickpoints which identified by the anomalous high values of SL/K,distribut along the faults on both sides of the north and south of the catchment.This indicates the strong activity of the faults in both north and south sides of the catchment.A couple of same elevations of knickpoints from different valleys crossing the fault in the north of the Wanchuan river show multi-period fault activity.The relationships of the distribution of knickpoints,faults and the lithostratigraphic boundary show the knickpoints in north are related to fault activity,while the knickpoints in south are not only controlled by tectonics,but partly affected by lithological differences.The tectonic information reflected by the distribution of knickpoints is confirmed by fault escarpment,crack,and triangular facet discovered in the field.2)The mountain front sinuosity index(SMF)in the northern part of Wanchuan River is 1.03?1.18,which show the straight front of the mountain.In addition,fault escarpment with 3-4 m height is found along the north side of the valley.These indicate neotectonic movement is quite active in the northern part of the Wanchuan River;the activity of Wanchuan river fault is also indicated by the small value,0.36-2.34,of the valley floor height-to-width ration(VF).The mean HI values,0.48 in north and 0.40 in south further indicate "youth" and/or "maturity" stage of the evolution of landscape in the catchment,and the rate of uplift is higher than rate of the river erosion in north.3)The abnormal AF index shows that there should be tilted fault block and folds in the northwest of Wanchuan river catchment.In addition,the strike-slip movement in the eastern part of the Wanchuan river fault is reflected by the offset of the valley crossing the fault.